In the competitive production of products, it is common to inspect the products with respect to performance, physical integrity, physical dimensions, cosmetic appearance, etc. before the products are sold. As competition becomes tighter, manufacturers move from classical manual labor intensive methods to more sophisticated techniques using automation. One of the newest techniques of automatic inspection or quality control is to use computer vision techniques by which a computer receives data from an optical system and processes the data to determine if a particular product passes inspection.
While electronic devices have long been tested internally by high-speed automatic testing and handling equipment, computer vision inspection systems are now being developed to inspect the outside of electronic packages. This task has proven considerably more difficult than testing the interior circuitry. Ideally, such systems should inspect both the package body and the leads that extend from the package body.
Developing an automated visual inspection system for a particular device requires careful design. First, there must be an objective, quantifiable visual test standard for the part. Commercial general purpose inspection systems are not trainable by presenting them with a collection of good and defective parts and a few general words of guidance. Second, the inspection requirements are used to specify the image acquisition parameters, such as lighting, background, the required image resolution. Very important is the size of the digital image sent to the computer. The greater the digital image, the larger the number of bits that must be stored and manipulated by the computer or processor, which slows the inspection time.
Third, an image analysis strategy must be designed, processing algorithms developed, and a classification scheme defined. Fourth, an appropriate parts handling mechanism is needed to present the parts to the vision system. Of course, the performance of any computer inspection system must be measured by comparing its results with the independently and presumably accurate parts classification prepared from the existing manual inspection.
However, the demonstration of a satisfactory method for inspecting a particular electronic package is not, by itself, a sufficient basis to use an automatic inspection system. For a production machine to be implemented, the inspection system must also meet cost, speed, reliability, and size constraints, as well as ease of integration with existing production methods.
It is only when all of the above requirements have been considered that a successful implementation of an automated visual inspection system can be achieved. In addition, it would be desirable if a particular inspection system could be readily adaptable to various electronic device packages. Such a system should also be able to be adapted to inspect other objects having a plurality of similar projecting features that need to have specified positions.